While advances in regenerative medicine have flourished, significant hurdles remain with respect to the commercial manufacture of consistent, uniform, reproducible tissue constructs. Relatively few products have realized commercial success as tissue substitutes despite significant advancements in the field of tissue engineering. Several challenges still remain for translating tissue-engineering technologies from bench to bedside. In addition to demonstrating clinical effectiveness, cost-effective manufacturing processes that comply with current quality and safety regulations are desirable. Failure to adequately consider the likely cost of manufacturing early in process and product development has been recognized as a limiting factor for commercial success of technologies in the field. Traditional manual laboratory tissue culture techniques are not economical at large clinical scales and have inherent variability and contamination risks. However, due to their widespread use, simplicity, minimal development time and low initial costs, these processes are often used to advance engineered tissues into clinical trials and the marketplace.
For example, CARTICEL, available from Aastrom Biosciences, Inc. (Ann Arbor, Mich.), is an autologous cell transplantation product used to repair articular cartilage injuries in the knee. CARTICEL is manufactured via manual techniques performed by trained technicians in a serologic clean room. Briefly, cells are isolated from the patient and expanded on tissue culture flasks to a sufficient number necessary for the desired therapeutic use. This process requires a large number of manual labor-intensive manipulation steps. Manual processes such as this, though perhaps more feasible and economical on a small-scale during early process development, are generally regarded as high risk due to the increased potential for contamination. Additionally, inherent differences in processing techniques between individuals, especially with technically challenging methods, can lead to process inconsistencies and end product variability. Furthermore, as production demand increases, scale-up would require multiple manual processes to be performed in parallel, thereby requiring additional technicians and generating substantial labor costs. As a result, the overall cost of production of such products tends to be high and can limit clinical success when the cost-benefit of the product is evaluated against competing, and often-simpler therapeutic strategies. Automating manual tissue-culture processes through use of bioreactor systems can provide a means to standardize culture processes, tightly control culture environments, remove user-dependent operation, and enable cost-effective tissue manufacturing processes to meet large-scale clinical demand.
Automated bioreactors have previously been used in tissue-engineering manufacturing and typically involve streamlining traditional two dimensional cell culture processes (e.g., cell selection, expansion, differentiation, etc.). While important, these cell manufacturing processes are often only the starting point for many tissue engineering strategies that utilize well characterized cell populations for tissue growth. Thus, there is a need to foster automated bioreactor-based systems fit for the development of reproducible three dimensional constructs. A closed, standardized, and operator-independent bioreactor system would have the potential to ensure safety and regulatory compliance and enable cost-effective, large-scale, in vitro tissue production.
Recently, Advance Tissue Science developed an automated system for large scale manufacturing of their human fibroblast derived dermal substitute, DERMAGRAFT (currently manufactured by Organogenesis, Inc. (Canton, Mass.)). DERMAGRAFT consists of living cryopreserved allogeneic dermal fibroblasts seeded onto a bio-absorbable polyglactin mesh scaffold used for treatment of chronic skin wounds such as diabetic foot ulcers. The entire manufacturing process is performed in a closed bioreactor bag, eliminating user-dependent variability and shielding the culture process from risk of contamination. Following injection of cells into the system, the bioreactor is only externally manipulated, until the graft is thawed and utilized in the operating room.
A single DERMAGRAFT bioreactor bag can be used to manufacture up to eight grafts, each in individual compartments. Additionally, twelve bags can be attached to an automated perfusion manifold system, standardizing culture parameters and allowing for up to 96 grafts to be made in a single production run. From a scientific perspective, the ability of an automated bioreactor system to systematically control and manipulate key culture parameters is important for providing data sets needed to standardize production methods and optimize end-product criteria. Though initial development costs of automated bioreactor systems are often high, the lack of user-dependence and ability to create large production volumes can greatly improve the long term cost effectiveness and commercial viability of the process. The lack of sufficient process control early in the DERMAGRAFT manufacturing process resulted in many defective products and ultimately contributed to overall high production costs. Thus, there is a need for process and manufacturing issues to be addressed earlier in product life cycle to increase likelihood of commercial success and clinical benefit. Failure to address manufacturing concerns early can lead to process changes later during pre-market approval that will likely require revalidation or additional studies to ensure safety and efficacy.
Current automated bioreactor systems such as the DERMAGRAFT are product specific and may pose problems for the fabrication of larger three-dimensional tissues. Moreover, no bioreactor currently exists for the fabrication of three-dimensional bone-ligament tissue constructs, such as those described in U.S. Pat. No. 8,764,828, assigned to the Applicant of the present application and hereby incorporated by reference in its entirety. To facilitate the manufacture of a wide-range of multi-phasic, three-dimensional tissue constructs, a novel bioreactor must be developed. As with current automated manufacturing systems, the bioreactor design should be user-independent, require only external manipulation, minimize contamination risk, and be scalable. It should also recreate the unique multi-step formation, technician-dependent processes often required when forming multi-phasic tissue constructs.
Transitioning the laboratory concepts and methods involved with the manufacture of multi-phasic tissue constructs into well-characterized medical products and processes is a significant challenge, commonly underestimated by researchers in tissue engineering and regenerative medicine fields. In addition to meeting regulatory requirements and ensuring the consistency and safety of the desired product, the manufacturing system must be scalable and cost-effective to be economically viable and displace current treatment options. Addressing manufacturing issues related to scale-out, quality control, and cost-effective production early in the research stage can overcome problems that typically slow development, limit investment, and escalate costs that limit the clinical translation and availability of various treatment methods to patients in need.